Cell-site location information ("CSLI") is location information generated by cellular phone providers that indicates which cell tower a particular phone was communicating with when a communication was made. United States v. Curtis, No. 17-1833, 2018 WL 4042631, at *1 (7th Cir. Aug. 24, 2018). It is capable of pinpointing a phone's location within 50 meters. Id. Because cell phones are in constant communication with the nearest cell site—often affixed to a cell tower—they can collect CSLI as frequently as several times a minute. Id.
In June 2018, in Carpenter v. United States, 138 S. Ct. 2206 (2018), the Supreme Court extended Fourth Amendment protection to CSLI and held that the government conducts a "search" when it accesses historical cell phone records that provide a comprehensive chronicle of the user's past movements. The Court concluded that the government must generally obtain a warrant supported by probable cause before acquiring such records and rejected application of the "third-party doctrine," even though the records at issue were held by a wireless carrier.
The Court declined to say whether there was "a limited period for which the Government may obtain an individual's historical CSLI free from Fourth Amendment scrutiny," deciding only that accessing seven days' or more worth of information was enough. Id. at 2217 n.3. In Carpenter, the prosecutors had obtained court orders under the Stored Communications Act ("SCA"), 18 U.S.C. § 2703, and those court orders purported to authorize the collection of the target's cell phone records. The Court said that SCA compliance did not matter, because the showing required by the SCA "falls well short of the probable cause required for a warrant." Id. at 2221. The Court remanded the case for further proceedings.
It should be noted that although the new rule announced in Carpenter applies retroactively to all cases on direct review or not yet final, this does not necessarily mean that the exclusionary rule applies. United States v. Williams, No. 2:17-cr-20758-VAR-DRG, 2018 WL 369585 (E.D. Mich. Aug. 2, 2018). In Williams, the court held that because the government relied in good faith on the existing law to obtain the CSLI records without a warrant, the exclusionary rule did not apply.